Typically, a transparent conductive film is used for a plasma display panel (PDP), a liquid crystal display (LCD) device, a light-emitting diode (LED), an organic electroluminescent device (OLED), a touch panel, a solar cell, a transparent heater, etc.
Such a transparent conductive film, having high conductivity (e.g. a sheet resistance of 1×103 Ω/sq or less) and high transmittance in the visible light range, is being utilized for electrodes in a variety of light-receiving and light-emitting devices, as well as solar cells, liquid crystal display devices, plasma display panels, and smart windows, and additional applications thereof include transparent electromagnetic wave-shielding members such as antistatic films and electromagnetic shielding films for windows for vehicles or buildings, and transparent heat-generating members such as solar reflective films, glass showcases, etc.
Examples of the transparent conductive film include a tin oxide (SnO2) film doped with antimony or fluorine, a zinc oxide (ZnO) film doped with aluminum or potassium, and a tin-doped indium oxide (In2O3) film.
In particular, a tin-doped indium oxide film, namely an In2O3—Sn film, which is referred to as an ITO (Indium tin oxide) film, is most commonly used because a low-resistance film may be readily acquired. Although ITO is superior in various properties and is mainly applied to processes, indium oxide (In2O3) is produced as a byproduct from zinc (Zn) mines, and thus the demand therefor and supply thereof are not balanced. Furthermore, an ITO film is not flexible and thus cannot be employed in flexible materials such as polymer substrates, and the production cost thereof is increased because of the manufacture under high-temperature and high-pressure conditions.
Also, the upper surface of a polymer substrate may be coated with a conductive polymer to obtain a flexible display, but the formed film may deteriorate electrical conductivity when exposed to the exterior environment, or may not be transparent, and the use thereof is limited.
With the goal of solving such problems, actively being studied are methods in which various kinds of substrates are coated with carbon nanotubes or metal nanowires as a one-dimensional structure, or alternatively, graphene, having a two-dimensional structure, may be synthesized using chemical vapor deposition and may then be transferred to the substrate. When the carbon nanotubes are provided in the form of a network-type transparent conductive film, junction resistance is very high, making it difficult to drastically lower sheet resistance. In the case where semiconductive carbon nanotubes are contained, they suffer in that they are sensitive to the external environment.
As for metal nanowires, the resistance of nanowires alone is very low and thus, even when they are provided in the form of a network-type transparent conductive film, sheet resistance is remarkably decreased compared to the case of carbon nanotubes. However, in the case where the diameter of the metal nanowires is decreased and the resistance occurring at a junction of the network is high, the junction may be undesirably melted and broken due to electrical influence. Furthermore, the metal nanowires may cause problems of haze and light reflection when applied to displays. Also, when they are applied to multilayered optoelectronic devices, superior characteristics are exhibited, as long as contact problems of upper and lower materials and work function matching problems are solved.
Therefore, in order to apply the metal nanowires to displays, touch panels, various optical devices, transparent heaters, etc., metal nanowire-based transparent conductive films having ensured electrical, optical and mechanical stabilities have to be provided. To this end, there is a need for a single-component carbon nanomaterial and metal nanowire hybrid transparent conductive film in which work function matching problems are solved and which has good dispersibility, even without the use of a dispersant.